Free piston engines are utilized to convert chemical energy to hydro-mechanical energy. This type of engine, for example, when designed to operate on hydrocarbon fuels such as diesel grade fuel oils, include a piston adapted to slidingly linearly reciprocate within a combustion cylinder provided with an intake air aperture, an exhaust air aperture, and a fuel injection device. The piston is connected to a piston shaft extending from the piston through the combustion cylinder wall along the axis of movement of the piston. The piston shaft is typically connected to a return piston operating coaxially with the combustion cylinder piston in a compression chamber. The return piston slidably linearly reciprocates in the compression chamber under the influence of a compression device, so as to ensure the action of the combustion cylinder piston. A frequency control device, either of a hydraulic or electronic nature, is typically provided to control the action of the return piston and thereby control the speed of operation of the free piston engine. The piston shaft is further typically connected to linearly operate a plunger reciprocally in a power chamber. Such a plunger is, for example, suitable for use as a fluid pump for the compression of hydraulic fluid, as an air compressor, or another similar device.
In operation, the piston moves within the combustion cylinder between a top dead center position which is the position which provides the minimum volume of the combustion chamber defined by the piston and combustion cylinder, and the bottom dead center position at which the combustion chamber is at its maximum volume. During a typical two-cycle operation, the compression device is actuated to provide pressure on the compression piston and act upon the combustion cylinder piston through the piston connecting rod to drive the combustion cylinder piston toward the top dead center position. As the piston approaches the top dead center position, the fuel injector is actuated to spray a quantity of fuel into the combustion chamber. Because of the relatively high compression caused by the piston within the combustion chamber, the fuel-air mixture then auto-ignites, causing the combustion cylinder piston to subsequently reverse its direction and move toward the bottom dead center position. A portion of the energy thus released by the fuel-air mixture combustion is recaptured in the return piston actuator device. However, the majority of the energy thus released is transmitted through the piston connecting rod to the plunger and thus to the fluid upon which the plunger acts. As the piston continues to move toward bottom dead center, the piston moves to open the exhaust aperture and the intake air apertures to permit the flow of exhaust gases from the combustion chamber and to permit a new inflow of intake air to be used in the succeeding engine cycle.
One primary disadvantage of the two-cycle free piston type engine, according to the prior art, has been the undesirable production of exhaust gas by-products such as NOx. Another undesirable feature of the two-cycle internal combustion engine has typically been the emission of undesirable quantities of unburned hydrocarbons. Many legal jurisdictions now regulate the various emissions and have established laws and regulations which provide legal sanction for the operation of engines with emissions in excess of the allowable standards. Also, some jurisdictions disallow the operation of such engines until modifications or repairs have been completed thereon. Therefore, it is desirable to improve the performance of internal combustion engines in this respect.
It is well known, that the production of NOx increases as a function of the local flame temperature of the air-fuel mixture during combustion thereof. Excessively high local flame temperature is typically a function of a failure to provide an adequate mixture of the air and fuel prior to combustion. However, injection of atomized fuel into the combustion chamber requires a finite time period for the delivery of the desired fuel volume, just as the entry of intake air and expunging of exhaust by-products requires a finite time period. The operating method according to the prior art typically provides only a short space of time for fuel-air mixing. When the air-fuel mixture is inadequately mixed, the proportion of unburned hydrocarbon likewise tends to increase due to the irregularity of the flame temperature through the combustion chamber.
It is therefore desirable to reduce the production of undesirable emission by-products in a free piston-type internal combustion engine with out adversely affecting the performance of the engine in which it is employed.
It is also desirable to reduce the production of undesirable emission by-products by providing a lower and more uniform local flame temperature in the combustion chamber of the engine in which it is employed.
It is also desirable to reduce the production of undesirable emission by-products without adding components or making modifications to the free piston engine.
The present invention is directed to overcoming one or more of the problems set forth above.